My first question, have you ever overrun your D3s buffer in actual use?
Have you overrun it with the 1000x cards?
If you can legitimately answer yes to either question as a real problem in your work, and you regularly need faster buffer clearing than the D3s, you need look into the D4. D4 gets far better write throughput by a combination of the new EXPEED engine and the XQD card write speed in camera. In camera 91MB/s as opposed to 62MB/s for CF. The combo writes faster than anything Nikon did previously, and it also writes faster to the same CF cards than the D3s. I attached the table at the bottom, from this review:
Of course, it is a bit slower if you overrun to the CF card. According to the tester below, on XQD he got 72 NEF lossless compressed shots at 11fps vs 66 shots into the CF card before slowdown. 6 more shots for the new card.
Now it is currently a different story for card to computer speed, the 1000x Lexars and reader are faster than the XQD, 116 to 129 MB/s. While this number matters to me more than the in camera (which as I said does not effect me), if you are shooting RAW in reality it is the total time of transfer and processing that matters, NOT just the transfer, so frankly even the slowest cards load in a comparative blink compared to the RAW processing. The transfer speeds do matter a lot to a jpeg PJ shooter, as they can work with images immediately upon their arrival at the computer.
For me, although I did suffer buffer overrun in the D3, the D3s never did this to me in practice. Of course I made it happen to see how many shots I could actually get before it slowed down sitting here at my desk, but never an issue in reality. Card to computer times are really not important, since I fit the whole performance's job on one card, and I have to import and process the RAW files, I would just start an import, go get a sandwich and start culling upon return, no big deal.
Once in a great while on location I will come back with 2-3 cards from multiple days (all cards are mirror, so actually double that) and those I stick in the ganged reader and copy to disk before the single large Aperture import. Maybe once a month.